# This program is copyright 2008-2011 Percona Ireland Ltd.
# Feedback and improvements are welcome.
#
# THIS PROGRAM IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED
# WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
# MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
#
# This program is free software; you can redistribute it and/or modify it under
# the terms of the GNU General Public License as published by the Free Software
# Foundation, version 2; OR the Perl Artistic License.  On UNIX and similar
# systems, you can issue `man perlgpl' or `man perlartistic' to read these
# licenses.
#
# You should have received a copy of the GNU General Public License along with
# this program; if not, write to the Free Software Foundation, Inc., 59 Temple
# Place, Suite 330, Boston, MA  02111-1307  USA.
# ###########################################################################
# Daemon package
# ###########################################################################
{
# Package: Daemon
# Daemon daemonizes the caller and handles daemon-related tasks like PID files.
package Daemon;

use strict;
use warnings FATAL => 'all';
use English qw(-no_match_vars);
use constant PTDEBUG => $ENV{PTDEBUG} || 0;

use POSIX qw(setsid);

# The required o arg is an OptionParser object.
sub new {
   my ( $class, %args ) = @_;
   foreach my $arg ( qw(o) ) {
      die "I need a $arg argument" unless $args{$arg};
   }
   my $o = $args{o};
   my $self = {
      o        => $o,
      log_file => $o->has('log') ? $o->get('log') : undef,
      PID_file => $o->has('pid') ? $o->get('pid') : undef,
   };

   # undef because we can't call like $self->check_PID_file() yet.
   check_PID_file(undef, $self->{PID_file});

   PTDEBUG && _d('Daemonized child will log to', $self->{log_file});
   return bless $self, $class;
}

sub daemonize {
   my ( $self ) = @_;

   PTDEBUG && _d('About to fork and daemonize');
   defined (my $pid = fork()) or die "Cannot fork: $OS_ERROR";
   if ( $pid ) {
      PTDEBUG && _d('Parent PID', $PID, 'exiting after forking child PID',$pid);
      exit;
   }

   # I'm daemonized now.
   PTDEBUG && _d('Daemonizing child PID', $PID);
   $self->{PID_owner} = $PID;
   $self->{child}     = 1;

   POSIX::setsid() or die "Cannot start a new session: $OS_ERROR";
   chdir '/'       or die "Cannot chdir to /: $OS_ERROR";

   $self->_make_PID_file();

   $OUTPUT_AUTOFLUSH = 1;

   # We used to only reopen STDIN to /dev/null if it's a tty because
   # otherwise it may be a pipe, in which case we didn't want to break
   # it.  However, Perl -t is not reliable.  This is true and false on
   # various boxes even when the same code is ran, or it depends on if
   # the code is ran via cron, Jenkins, etc.  Since there should be no
   # sane reason to `foo | pt-tool --daemonize` for a tool that reads
   # STDIN, we now just always close STDIN.
   PTDEBUG && _d('Redirecting STDIN to /dev/null');
   close STDIN;
   open  STDIN, '/dev/null'
      or die "Cannot reopen STDIN to /dev/null: $OS_ERROR";

   if ( $self->{log_file} ) {
      PTDEBUG && _d('Redirecting STDOUT and STDERR to', $self->{log_file});
      close STDOUT;
      open  STDOUT, '>>', $self->{log_file}
         or die "Cannot open log file $self->{log_file}: $OS_ERROR";

      # If we don't close STDERR explicitly, then prove Daemon.t fails
      # because STDERR gets written before STDOUT even though we print
      # to STDOUT first in the tests.  I don't know why, but it's probably
      # best that we just explicitly close all fds before reopening them.
      close STDERR;
      open  STDERR, ">&STDOUT"
         or die "Cannot dupe STDERR to STDOUT: $OS_ERROR"; 
   }
   else {
      if ( -t STDOUT ) {
         PTDEBUG && _d('No log file and STDOUT is a terminal;',
            'redirecting to /dev/null');
         close STDOUT;
         open  STDOUT, '>', '/dev/null'
            or die "Cannot reopen STDOUT to /dev/null: $OS_ERROR";
      }
      if ( -t STDERR ) {
         PTDEBUG && _d('No log file and STDERR is a terminal;',
            'redirecting to /dev/null');
         close STDERR;
         open  STDERR, '>', '/dev/null'
            or die "Cannot reopen STDERR to /dev/null: $OS_ERROR";
      }
   }

   return;
}

# The file arg is optional.  It's used when new() calls this sub
# because $self hasn't been created yet.
sub check_PID_file {
   my ( $self, $file ) = @_;
   my $PID_file = $self ? $self->{PID_file} : $file;
   PTDEBUG && _d('Checking PID file', $PID_file);
   if ( $PID_file && -f $PID_file ) {
      my $pid;
      eval {
         chomp($pid = (slurp_file($PID_file) || ''));
      };
      if ( $EVAL_ERROR ) {
         # Be safe and die if we can't check that a process is
         # or is not already running.
         die "The PID file $PID_file already exists but it cannot be read: "
            . $EVAL_ERROR;
      }
      PTDEBUG && _d('PID file exists; it contains PID', $pid);
      if ( $pid ) {
         my $pid_is_alive = kill 0, $pid;
         if ( $pid_is_alive ) {
            die "The PID file $PID_file already exists "
               . " and the PID that it contains, $pid, is running";
         }
         else {
            warn "Overwriting PID file $PID_file because the PID that it "
               . "contains, $pid, is not running";
         }
      }
      else {
         # Be safe and die if we can't check that a process is
         # or is not already running.
         die "The PID file $PID_file already exists but it does not "
            . "contain a PID";
      }
   }
   else {
      PTDEBUG && _d('No PID file');
   }
   return;
}

# Call this for non-daemonized scripts to make a PID file.
sub make_PID_file {
   my ( $self ) = @_;
   if ( exists $self->{child} ) {
      die "Do not call Daemon::make_PID_file() for daemonized scripts";
   }
   $self->_make_PID_file();
   # This causes the PID file to be auto-removed when this obj is destroyed.
   $self->{PID_owner} = $PID;
   return;
}

# Do not call this sub directly.  For daemonized scripts, it's called
# automatically from daemonize() if there's a --pid opt.  For non-daemonized
# scripts, call make_PID_file().
sub _make_PID_file {
   my ( $self ) = @_;

   my $PID_file = $self->{PID_file};
   if ( !$PID_file ) {
      PTDEBUG && _d('No PID file to create');
      return;
   }

   # We checked this in new() but we'll double check here.
   $self->check_PID_file();

   open my $PID_FH, '>', $PID_file
      or die "Cannot open PID file $PID_file: $OS_ERROR";
   print $PID_FH $PID
      or die "Cannot print to PID file $PID_file: $OS_ERROR";
   close $PID_FH
      or die "Cannot close PID file $PID_file: $OS_ERROR";

   PTDEBUG && _d('Created PID file:', $self->{PID_file});
   return;
}

sub _remove_PID_file {
   my ( $self ) = @_;
   if ( $self->{PID_file} && -f $self->{PID_file} ) {
      unlink $self->{PID_file}
         or warn "Cannot remove PID file $self->{PID_file}: $OS_ERROR";
      PTDEBUG && _d('Removed PID file');
   }
   else {
      PTDEBUG && _d('No PID to remove');
   }
   return;
}

sub DESTROY {
   my ( $self ) = @_;

   # Remove the PID file only if we created it.  There's two cases where
   # it might be removed wrongly.  1) When the obj first daemonizes itself,
   # the parent's copy of the obj will call this sub when it exits.  We
   # don't remove it then because the child that continues to run won't
   # have it.  2) When daemonized code forks its children get copies of
   # the Daemon obj which will also call this sub when they exit.  We
   # don't remove it then because the daemonized parent code won't have it.
   # This trick works because $self->{PID_owner}=$PID is set once to the
   # owner's $PID then this value is copied on fork.  But the "== $PID"
   # here is the forked copy's PID which won't match the owner's PID.
   $self->_remove_PID_file() if ($self->{PID_owner} || 0) == $PID;

   return;
}

sub slurp_file {
   my ($file) = @_;
   return unless $file;
   open my $fh, "<", $file or die "Cannot open $file: $OS_ERROR";
   return do { local $/; <$fh> };
}

sub _d {
   my ($package, undef, $line) = caller 0;
   @_ = map { (my $temp = $_) =~ s/\n/\n# /g; $temp; }
        map { defined $_ ? $_ : 'undef' }
        @_;
   print STDERR "# $package:$line $PID ", join(' ', @_), "\n";
}

1;
}
# ###########################################################################
# End Daemon package
# ###########################################################################